Can inhaled cannabis users accurately evaluate impaired driving ability? A randomized controlled trial.
Sarah Hartley, Nicolas Simon, Bibiana Cardozo, Islam Amine Larabi, Jean-Claude Alvarez
Frontiers in Public Health 2023 DOI: 10.3389/fpubh.2023.1234765 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Controlled crossover experiment Randomized Peer reviewed |
|---|---|
| Sample size | 30 |
| Population | Healthy male volunteers aged 18-34; 15 chronic (1-2 joints/day) and 15 occasional (1-2 joints/week) cannabis consumers |
| Interventions | THC mixed with tobacco in a cigarette Placebo |
| Dose | 10 mg or 30 mg of THC |
| Duration | Measurements before and repeatedly after inhalation, with follow-up to 8 hours |
| Measures | Visual analog scale (driving confidence), Karolinska vigilance scale, mean reciprocal reaction time (mRRT) from the psychomotor vigilance test, standard deviation of lane position (SDLP) on a York driving simulator, blood THC concentrations |
| Topics | Cannabis |
| Keywords | Accident Driving simulator Reaction time |
| Registration | NCT02061020 |
| Key findings | Inhaled THC at 10 mg and 30 mg produced a marked decrease in driving confidence over the first 2 hours that remained below baseline at 8 hours, related to THC dose and blood concentration (EC50 0.11 ng/ml, half-time 37 min). Driving ability on a simulator and reaction times were reduced, and driving confidence was related to both in chronic and occasional consumers. |
Abstract
To study the effect of inhaled cannabis on self-assessed predicted driving ability and its relation to reaction times and driving ability on a driving simulator. 30 healthy male volunteers aged 18-34: 15 chronic (1-2 joints /day) and 15 occasional (1-2 joints/week) consumers. Self-assessed driving confidence (visual analog scale), vigilance (Karolinska), reaction time (mean reciprocal reaction time mRRT, psychomotor vigilance test), driving ability (standard deviation of lane position SDLP on a York driving simulator) and blood concentrations of delta-9-tétrahydrocannabinol (THC) were measured before and repeatedly after controlled inhalation of placebo, 10 mg or 30 mg of THC mixed with tobacco in a cigarette. Cannabis consumption (at 10 and 30 mg) led to a marked decrease in driving confidence over the first 2 h which remained below baseline at 8 h. Driving confidence was related to THC dose and to THC concentrations in the effective compartment with a low concentration of 0.11 ng/ml for the EC50 and a rapid onset of action (T1/2 37 min). Driving ability and reaction times were reduced by cannabis consumption. Driving confidence was shown to be related to driving ability and reaction times in both chronic and occasional consumers. Cannabis consumption leads to a rapid reduction in driving confidence which is related to reduced ability on a driving simulator. ClinicalTrials.gov, identifier: NCT02061020.
Comparable studies
Other randomized controlled trials on cannabis, most cited first.
| Study | Year | Design | Participants |
|---|---|---|---|
| Cannabidiol inhibits THC-elicited paranoid symptoms and hippocampal-dependent memory impairment Healthy participants | 2012 | Randomized controlled trial | n = 48 |
| Distinct Effects of Δ9-Tetrahydrocannabinol and Cannabidiol on Neural Activation During Emotional Processing Healthy, English-native, right-handed men who had used cannabis 15 times or less in... | 2009 | Double-blind, randomized, placebo-controlled crossover trial | n = 15 |
| Acute Effects of a Single, Oral dose of d9-tetrahydrocannabinol (THC) and Cannabidiol (CBD) Administration in Healthy Volunteers Healthy male subjects | 2012 | Randomized controlled trial | n = 16 |
| Modulation of Mediotemporal and Ventrostriatal Function in Humans by Δ9-Tetrahydrocannabinol Healthy, native English-speaking, right-handed men of white race/ethnicity who had used... | 2009 | Randomized controlled trial | n = 15 |
| Cannabidiol (CBD) content in vaporized cannabis does not prevent tetrahydrocannabinol (THC)-induced impairment of driving and cognition Healthy volunteers with a history of light cannabis use | 2019 | Randomized, double-blind, within-subjects crossover | n = 14 |
Citations in the library
Cited by 2
- Experimental and observational evidence on substance use and metacognition among adults: a systematic review. Addictive Behaviors August 1, 2026
- Understanding cannabis use and car crashes: Insights from a randomized trial using a driving simulator on THC blood levels and subjective measures of sleepiness and performance. Journal of safety research December 1, 2025
Cites 6
- Smoked Cannabis' Psychomotor and Neurocognitive Effects in Occasional and Frequent Smokers Journal of Analytical Toxicology March 4, 2015
- Driving Performance and Cannabis Users' Perception of Safety: A Randomized Clinical Trial. JAMA Psychiatry March 1, 2022
- Cannabis effects on driving longitudinal control with and without alcohol. Journal of Applied Toxicology November 2016
- Weed or Wheel! fMRI, Behavioural, and Toxicological Investigations of How Cannabis Smoking Affects Skills Necessary for Driving PLoS One January 2, 2013
- Neurocognitive performance during acute THC intoxication in heavy and occasional cannabis users. Journal of Psychopharmacology May 2009
and 1 more in the library